1. Field of the Invention
The present invention relates to an electrolytic capacitor, and a method of producing such an electrolytic capacitor.
2. Description of Related Art
In accordance with digitization of electronic equipment, the capacitor employed therein is required to be compact with a large capacitance, as well as having a small equivalent series resistance (hereinafter, abbreviated as ESR) in the high frequency region.
Conventionally, capacitors for high frequency regions include plastic film capacitors, laminated ceramic capacitors, and the like, all having a relatively small capacitance.
As a compact capacitor of large capacitance, having a relatively low ESR, there is known an electrolytic capacitor employing electron conductive material such as manganese dioxide, TCNQ (7,7,8,8-tetracyanoquinodimethane) complex salt, or the like for the cathode material. In recent years, there is also known the usage of an electrolytic capacitor including a conductive solid layer formed of conductive polymer such as polypyrrole, polythiophene, polyfuran, polyaniline and the like for the cathode.
The structure of an electrolytic capacitor including a conductive solid layer in the cathode includes the type having a dielectric film formed on the surface of an anode sintered compact or anode foil made of a valve action metal such as aluminum, tantalum or the like and further having a conductive solid layer, a graphite layer, and a silver paint layer sequentially formed thereon. There is also the so-called wound-type electrolytic capacitor having a conductive solid layer formed on a dielectric film of a capacitor element made by winding an anode foil such as of aluminum with the dielectric film at the surface and an opposite cathode foil together with a separator therebetween, impregnated with an electrolyte, as necessary.
For example, Japanese Patent Laying-Open No. 02-015611 discloses an electrolytic capacitor including a specific polythiophene for the solid electrolyte. With regards to a wound-type electrolytic capacitor, Japanese Patent Laying-Open No. 11-186110, for example, teaches an electrolytic capacitor produced by the steps of impregnating a wound-type capacitor element with monomer forming conductive polymer, and immersing the same in an aqueous solution of an oxidizing agent such as ammonium persulfate to cause chemical oxidative polymerization of the monomer to form the conductive polymer. Japanese Patent Laying-Open No. 2005-322917 discloses an electrolytic capacitor produced by the steps of introducing a mixture of a precursor and an oxidizing agent directed to production of conductive polymer into a porous electrode body covered with a dielectric layer, exposing the porous electrode body impregnated with the mixture of the precursor and oxidizing agent to a certain relative humidity to cause polymerization of the precursor to form a solid electrolyte.
However, none of the electrolyte capacitors set forth above have sufficient withstand voltage, as well as a low ESR of a satisfactory level.